Transmission x-ray scanners used for personnel screening already exist in the market and are used in high-security areas where access is restricted from the general public, such as prisons, diamond and gold mines, and other places where small, high-value or dangerous items can be smuggled into or out from a secure area. One such system is described in U.S. Pat. No. 7,397,892 B2 to Linev, which issued on Jul. 8, 2008, and is incorporated herein in its entirety. Linev teaches the use of an x-ray source that produces a single, fan-shaped x-ray beam that is collimated to produce a vertical beam of x-rays that is further collimated down to a very narrow slit. These collimated x-rays illuminate a single linear array of photo diodes coated with a scintillating phosphor. The person to be scanned stands on a motor-driven platform that moves the person slowly in between the source and the diode detector array exposing their entire body to the x-ray beam, thereby producing an x-ray image of their entire body. The x-ray image then reveals any objects they may have ingested, hidden in their clothing, or inserted in a body cavity.
The system taught by Linev, while effective because it can reveal the hidden items described above, suffers from a number of limitations. One of the primary limitations that the preferred embodiment of the Linev system suffers from is the inability to scan someone who has difficulty standing or is in a wheelchair. The platform (described in Linev as a walk-gate floor or movable door that is moving at constant speed) that is used to move the person being screened across the x-ray beam is small and difficult to access. It would, then, be a simple matter for a person to circumvent the scanner by claiming to need crutches, a walker, or a wheelchair. The scanning speed of the platform is necessarily slow to prevent the person standing on the platform from falling down or being injured. The slow scanning speed reduces throughput of the system and, thereby, the rate at which people can be scanned. Another limitation of this system is that x-ray radiation scattered from the person being scanned exposes anyone in the vicinity of the system to harmful radiation. This is because the system taught by Linev does not fully enclose and shield the walk-gate area. To mitigate this problem, a large exclusion area around the system must be established. This exclusion area greatly increases the amount of space required and increases the cost to install and operate the system. Any rooms adjacent to or in the floors above or below the system would also be similarly affected by this scattered radiation.
Yet another disadvantage of the system taught by Linev is a lack of control of the amount of radiation dose to which the person being scanned is exposed. The Linev system teaches the use of a fixed collimator and a detector positioning system. The exposure dose to the person being scanned is greatly affected by the accuracy in which the x-ray beam covers the detector array. If the width of the collimated fan beam of the x-ray source is larger than the width of the detector array, then x-rays that do not contribute to the image being formed are exposing the person being scanned, causing excess and unwarranted x-ray exposure. Linev also does not teach the use of varying the x-ray beam technique to optimize exposure parameters for each person being scanned. An x-ray beam technique refers to the x-ray energy (kVp), the integrated intensity (mAs), and the filtration used to acquire the image. If these x-ray exposure parameters are not adjusted to the specific body mass and anatomical region being scanned, then the exposure used to acquire the image is not optimal and, consequently, the dose used to acquire the image is not minimized. This could result in over-exposure or require a repeat exposure if the parameters are inadequate for an acceptable image (underexposure).
Yet another disadvantage of the system taught by Linev is the inability to create different configurations of the system that could provide flexibility in the installation and use of the system in different facilities. There are places, for example, such as office buildings, hotels, and private residences where the need for security exists but the physical presence of x-ray systems and equipment creates problems with available space and a desire to obscure or hide the security apparatus from view.